Deformable-elastic intraocular lens

ABSTRACT

A deformable-elastic intraocular lens comprising a deformable-elastic lens body of crosslinked acrylic material formed of copolymers of methacrylate and acrylate esters which are relatively hard and relatively soft at body temperature, crosslinked with a diacrylate ester to produce an acrylic copolymer having a substantially tack-free surface, a crosslink density of between . .0.5×10 -2  and 1.5×10 -2  .!. .Iadd.0.23×10 -1  and 1.66×10 -1  .Iaddend.moles per liter, and glass transition temperature in the range of -30° C. to 25° C., a tensile modulus between 1000 and 3000 psi and a elongation a break of 100% or greater.

BACKGROUND OF THE INVENTION

The present invention relates generally to improvements in intraocularlenses (IOLs) designed for surgical implantation into the eye, forexample, as a replacement for a cataractous or injured natural lens.More specifically, the invention relates to improvements in deformableIOLs which can be folded or rolled to a relatively low profile size tofit into the eye through a relatively small incision, and then withinthe eye naturally return to an internal nondeformed shape withpredetermined optical properties.

IOLs are well known in the art for implantation into the eye as areplacement for a natural crystalline lens which has been surgicallyremoved typically due to opacification, commonly referred to as acataract condition. Such IOLs have been formed from a small disk oftransparent glass or plastic material having appropriately shaped lenssurfaces to achieve a desired set of optical properties. The IOL isimplanted directly into the eye, typically after removal of the naturalcrystalline lens, via an incision formed in ocular tissue such as thescalera outside the normal line of sight. Many IOLs are designed forimplantation into the so-called posterior chamber of the eye behind theiris and pupil, whereas other IOLs are adapted for placement into theanterior chamber in front of the iris and pupil. In most IOL designs,support structures are attached to or formed integrally with a centrallens body or optic and project outwardly therefrom to contact eye tissueat the periphery of the posterior or anterior chamber, thereby retainingthe lens body or optic in generally centered relation with the line ofsight passing through the pupil.

In the past, most IOLs have been formed from polymethylmethacrylate(PMMA) which is relatively light in weight, possesses excellent opticalproperties, and is generally considered to be relatively inert whenimplanted into the eye, thereby avoiding adverse tissue reactions.However, PMMA comprises a plastic matrix which, when formed into theshape of a lens, possesses high rigidity and cannot be deformed byfolding, rolling, compression, etc. Accordingly, the use of PMMA lensesrequires a relatively large incision in the ocular tissue sufficient toaccommodate the entire diametric size of the lens body; which istypically six millimeters or larger, together with the accompanying lenssupports structures. Although the resilient lens support structures sucha polypropylene loops or haptics are commonly used and advantageouslymay be folded over the lens body during insertion, such resilienthaptics are anchored into the periphery of the hard plastic lens bodyand thus tend to spring back to their initial unfolded shape with arapid snap like action during IOL implantation, resulting in undesiredtrauma to sensitive eye tissues.

While IOLs with rigid PMMA lens bodies have gained widespread acceptanceand use, it has been recognized that deformable IOLs have the potentialof providing medical benefits well beyond those associated with currentIOLs including rigid lens bodies. More particularly, an IOL including adeformable transparent lens body which may be folded or rolled into areduced profile size may fit through a relatively small incision inocular tissue and after insertion and release within the eye return toits original size and shape by virtue of its natural resilience. The useof a smaller incision would beneficially result in a safer overallsurgical procedure requiring fewer stitches and reduced likelihood ofpostoperative complications such as infections. In addition, a smallerincision would reduce the incidence of postoperative astigmatism andsubstantially reduce rehabilitation time. Second, it is anticipated thatIOLs with deformable lens bodies may reduce the potential forcomplications secondary to contact or rubbing against delicate uvealtissues. Also, deformable IOLs may decrease the potential for pigmentarydispersion or pigmentary glaucoma. Finally, it is anticipated that theformable IOLs will provide an added margin of safety for patients withblood dyscarsias, coagulopalthies and hematologic matogrant disease aswell as those patients being given anti-coagulant therapy.

Accordingly, deformable IOLs formed of silicones and hydrogels have beenproposed for implantation. For example, in 1983, Fyodorov reported onchemical testing of a silicone IOL (Fyodorov, S. W. et al "InitialClinical Testing of a Silicone Intraocular Lens" InterzonalScientific/Practical Conference of Ophthalmologists of Western andEastern Siberia and the Far East, Conference Proceedings 4: 22-24, 1983,Vladivostock). Also in 1983, Mazzacco and Davidson presented initialdata on the implantation of silicone IOLs with 6 mm optical zonesthrough 3 mm incisions (Mazzacco, T. R. and Davidson, V. A. "6 mm Opticfor a 3 mm Wound" presented at the A.I.O.I.S. United States IntraocularLens Symposium, New Orleans, La., March 1983). Wichterle and hisassociates developed a hydrogel of hydrophilic polyacrylates for orbitaland intracameral implants in 1960 while Epstein implanted flexible IOLscomprised of poly(hydro hydroxyethyl methacrylate) in 1976 and 1977. Thecondition of some patients implanted with such lens was followed until1984 ("Insertion Techniques and Clinical Experience with HEMA Lenses"Soft Implant Lenses in Cataract Surgery T. R. Mazzacco, G. M. Rajacich,E. Epstein, published by Slack Inc., 1986, pp. 11).

Unfortunately, silicones and hydrogels have several well documenteddeficiencies which hinder their use as IOL materials. In particular,silicones cause complement activation leading to the production of C-4proteins, a symptom of bio-incompatibility. Also, while silicones may befolded, when released they tend to snap back or regain their unfoldedshape too rapidly, posing a threat to the integrity of the endothelialcell layer of the eye. In addition, the long term stability ofUV-absorbing silicone formulations is uncertain. As for hydrogels, ithas been found that hydrogel materials when hydrated vary in compositionincluding water content from lot to lot. Such variability induces acorresponding variability in the refractive power of IOL lens bodiesformed of hydrogel material. Therefore, hydrogel IOLs need to behydrated in order to determine their refractive power in implantedstate. Unfortunately, hydrated lenses cannot be safely stored in the wetstate without losing sterilization. If they are dehydrated subsequently,the process of hydrothermal cycling reduces the tensile strength of theIOL material and may cause cracks or crazes to develop in the lens body.

Other deformable IOLs have been described in U.S. Pat. Nos. 4,573,998and 4,608,049. More specifically, the '998 patent is directed to methodsfor implantation of deformable IOLs. The patent describes an IOL havingan optical zone portion composed of materials such as polyurethaneelastomers, silicone elastomers, hydrogel polymer collagen compounds,organic or synthetic gel compounds and combinations thereof. Inpractice, such materials possess the disadvantages previously attributedto silicone and hydrogen materials.

The '049 patent describes two basic types of deformable IOLs. The firstype includes a lens body of one or more rigid portions hinged orotherwise connected to overlap each other when it is desired to reducethe profile of thelens body as during implantation of the lens. Suchlens configurations are difficult to construct and to manipulate duringimplantation and further suffer from the limitations associated withrigid IOLs. The second type of IOL described by the '049 patent includesa deformable lens body characterized as being capable of return to anundeformed configuration after insertion into the eye. The lens body maybe of silicone rubber or an acrylate polymer with ethylene glycoldimethacrylate as a crosslinking agent producing a material of a rubberconsistency. The deformable lens body is secured to an L-shaped fixationmember around which it may be curled during insertion into the eye. Thesilicone rubber IOL of the '049 patent suffers from the limitationspreviously attributed to silicone IOLs. The acrylate polymer lens bodydescribed in the '049 patent is a hydrogel of a relatively hardconsistency (subject to the foreign problems attributed to hydrogels)while other acrylate polymers known to be pliable are prone tomechanical failure upon compression or folding and are subject todegradation in the eye.

In viewing of the foregoing, it is apparent that there is a need for anintraocular lens and lens material having an improved balance ofsuperior optical characteristics, flexibility, elasticity, elasticmemory, and tensile strength. The present invention satisfies suchneeds.

SUMMARY OF THE INVENTION

Generally speaking, the present invention comprises an IOL having adeformable-elastic transparent lens body of crosslinked acrylic materialhaving a tensile strength sufficient to resist deformation afterimplantation into the eye as by forces exerted by growing tissue aroundthe IOL; a flexibility as measured by elongation at break sufficient toallow the lens body to be readily folded, rolled or otherwise deformedto a low profile condition for implantation through a small incisioninto the eye; an elastic memory which enables the folded lens body tonaturally and at a controlled rate return to its original shape andoptical resolution without damaging or otherwise traumatizing eyetissue; and a low-tack surface which will not stick to surgicalinstruments used to hold and guide the lens body during insertion andpositioning within the eye. In particular, the crosslinked acrylicmaterial comprises copolymers of methacrylate and acrylate esters whichare relatively hard and relatively soft at body temperature, crosslinkedwith a diacrylate ester to produce an acrylic material having asubstantially tack-free surface, a crosslink density between . .0.5×10⁻²and 1.5×10⁻² .!. .Iadd.0.23×10⁻¹ and 1.66×10⁻¹ .Iaddend.moles per liter,a glass transition temperature in the range of -30° and 25° C., atensile modulus in the range of 1000 to 3000 psi and an elongation at abreak between 100 and 300%. Such a lens body is easily folded, rolled orotherwise deformed into a low profile for insertion through a smallincision and after insertion will naturally return to its originaloptical resolution at a slow controlled rate in between 20 and 180seconds even if the lens body has been deformed to a low profilecondition for an extended period of time. The slow return allows thesurgeon adequate time to locate the folded IOL in the eye before thelens body returns to its original shape and resolution and insures thatthe unfolding of the lens will not damage or otherwise traumatize oculartissue. Furthermore, a lens body of the foregoing material andcomposition possesses a desired tensile strength to resist deformationin response to forces exerted by tissue growing around the implantedlens body thereby maintaining the desired optical characteristics andresolution of the lens body.

Preferably, in the formation of the deformable-elastic acrylic material,the copolymers of methacrylate and acrylate esters are mixed atapproximately a 45 to 55 weight percent ratio and the relatively hardmethacrylate ester is a fluoroacrylate. The fluoroacrylate functions asa surface energy lowering agent as well as a monomer providing long termstable inertness and tensile strength to the polymer without adverselyeffecting the pliancy of the resulting material. In this regard, thefluoroacrylate is present in a concentration range by weight of between5 and 25% and preferably is trifluoro ethyl methacrylate. Also in thepreferred formulation of the crosslinked acrylic, the mixture of thecopolymers is partially polymerized prior to chemical crosslinking withdiacrylate ester in a concentration range of between 0.5 and 3.0 percentby weight.

The resulting crosslinked acrylic material may be molded and formed intolens bodies machined to have the desired optical characteristics andresolution with haptics extending therefrom either integral with orseparately attached to the lens body. Preferably, the crosslinkedacrylic material formed according to the present invention is machinedand otherwise processed at low temperatures in the range of -80° to -10°C. and preferably at -60° C. In particular, during cutting the lens bodyis maintained at a temperature below its Beta-relaxation temperaturewhere the material is even harder than at its glass transitiontemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a front elevation view of an exemplary IOL formed inaccordance with the novel features of the invention;

FIG. 2 is a side elevation view of the IOL depicted in FIG. 1;

FIG. 3 is a fragmented front elevation view depicting the IOL of FIG. 1implanted into the posterior chamber of an eye;

FIG. 4 is an enlarged perspective view illustrating the lens of FIG. 1rolled into a reduced size profile prior to implantation;

FIG. 5 is a fragmented sectional view illustrating implantation of thelens into the posterior chamber of the eye;

FIG. 6 is a graphic representation of the relative stiffness of the bodyof the IOL as a function of temperature;

FIG. 7 is a flow diagram in block form illustrating a preferred form ofa method for producing a deformable-elastic acrylic material comprisinga lens body of an IOL in accordance with the present, invention;

FIGS. 8A and 8B illustrate two molds useful in the method of the presentinvention for forming acrylic material into intraocular lens bodies; and

FIG. 9 is a plan view of a bottom part of a mold useful in forming a onepiece IOL in accordance with the present invention. FIG. 9 alsoillustrates a plan view of the part produced from such a mold.

DETAILED DESCRIPTION

As shown in the exemplary drawings, one preferred form of an improvedIOL is referred to generally by the reference numeral 10 in FIGS. 1-5.The improved lens 10 is deformable (FIGS. 4 and 5) to a reduced profilesize to permit implantation into an eye 12 through a relatively smallincision 14. The lens 10 is formed with a selected set of physicalcharacteristics to expand within the eye slowly but substantiallycompletely to its initial nondeformed state and optical resolutionwithout trauma to delicate eye tissue.

As shown in FIGS. 1, 2 and 3, the IOL 10 of the present inventioncomprises a traditional disk-shaped lens body 16 having an appropriatediametric typically on the order of about six millimeters and acombination of surface shapes on the anterior-posterior sides to provideselected dioptic characteristics, with a convexo-plano shape being shownby way of example in the illustrative drawings. The IOL 10 is adaptedfor implantation into the eye 12 subsequent to surgical removal of thenatural crystalline lens, typically due to a cataract conditions.Alternately, if desired, the IOL can be implanted to obtain refractivecorrection of the natural lens. Support structures such as a pair ofoutwardly radiating and curved resilient loops or haptics 18 are securedto the lens body 16 and function to support the lens body within the eye12, as will be described in more detail. The haptics 18 may beanteriorly angulated as shown in FIG. 2, and/or provided into otherconfigurations such as a trio of loops or alternate support structuresformed integrally with the lens body, in accordance with the particularintraocular lens design.

In accordance with known intraocular lens implantation techniques, theIOL 10 is adapted for implantation into the eye through an incision 14formed in the ocular tissue at a position removed from a normal sightline passing through the transparent cornea 19, as viewed in FIG. 5, andfurther through the pupil 20 defined by the iris 22. The IOL 10 can bedesigned as shown in FIG. 5 for implantation through the pupil 20 intoto so-called posterior chamber 24 behind the iris 22, typically within acapsular bag 26 which has been anteriorly ruptured in the course ofextracapsular extrusion of the natural crystalline lens. Alternately, ifdesired, the IOL 10 can be implemented into the anterior chamber 28 atthe front side of the iris 22. In either case, support structures suchas the illustrative pair of outwardly curing support loops 18 seatagainst surrounding tissue at the chamber periphery of retain the lensbody 16 generally centered on the normal line of sight. Positioningholes 32 may also be provided near the periphery of the lens body 16 andare easily engaged by appropriate surgical instruments (not shown) tofacilitate lens manipulation by the surgeon to the desired positionwithin the eye.

In accordance with primary aspects of the invention, the lens body 16 ofthe IOL is formed from a deformable-elastic transparent crosslinkedacrylic material with a unique balance of flexibility, elasticity,tensile strength and softness properties yielding significant advantagesduring implantation and subsequent use. More specifically, because ofits improved flexibility, the IOL is capable of being reduced in profilesize to fit through the incision 14 of reduced size in comparison withconventional hard plastic lens of polymethylmethacrylate (PMMA) or thelike. Because of its controlled elasticity, the lens body 16 anchors thehaptics 18 with sufficient damping to prevent rapid or snap-actionmovement of the haptics 18 toward their normal unstressedconfigurations, thereby preventing the haptics from sharply striking anddamaging eye tissue. Moreover, the lens body possess a relatively slowspeed of return or retraction of about twenty (20) to one-hundred eighty(180) seconds from a deformed state as shown in FIG. 4 to its initialundeformed state to avoid striking and damaging eye tissue. Further, thelens body has excellent elastic memory to insure substantially completereturn to the undeformed state without plastic deformation.in the formof fold lines or creases or other distortions which would otherwiseimpair optical quality.

The preferred crosslinked acrylic material for the IOL 10 comprisescopolymers of methacrylate and acrylate esters which are relatively hardand relatively soft at body temperature, partially polymerized,chemically crosslinked with a diacrylate ester and cured. The resultingacrylic has a relatively leathery characteristics at temperatureconditions corresponding with or approximating body temperature. Morespecifically, with reference to FIG. 6, the crosslinked acryliccomposition is selected to have a glass transition temperature (Tg)somewhat below body temperature so that the lens will exhibit astiffness (Young's modulus) at a body temperature environment reflectinga relatively leathery characteristic. In addition, the crosslinkedacrylic composition is chosen to have highly elastic or viscoelasticproperties with substantially no plastic deformation and a relativelyslow speed of retraction. With such a combination of characteristics,the IOL 10 can be deformed as by rolling upon itself together with thehaptic 18 as viewed in FIGS. 4 and 5 for facilitated implantation via asmall insertion tube 36 passed through the small incision 14. Inparticular, the hollow insertion tube 36 may be prefilled with Healon orthe like for lubrication purposes. The IOL 10, including the lens body16 and haptics 18, may be temperature prepared in advance substantiallyat body temperature, at which time the IOL 10 and tube 36 are advancedthrough the incision 14 and into the eye, for example, within theposterior chamber 24, where the lens is expelled from the tube 36 withinthe eye. The thus-released lens is allowed to return to its initialnondeformed state. Importantly, this return movement takes place slowlywith excellent elastic memory over a time of at least about twentyseconds. When the lens is substantially completely expanded, the lensposition within the eye can be manipulated with appropriate instrumentsengaging, for example, the positioning holes 32 after which the incisionis closed to complete the procedure.

The preferred lens body composition is prepared by copolymerization oftransparent acrylic and methacrylic monomers which otherwise exhibitrelatively hard and relatively soft physical characteristics in a bodytemperature environment and a glass transition temperature (Tg) withinthe range of about -30° to about 25° C. and more preferably 0° C.Preferably, the monomers include a fluorometer for enhancing thetack-free inertness and tensile strength of characteristics of the lensbody within the eye and the resulting acrylic is produced by chemicalcrosslinking with a diacrylate ester to form a stable interpenetratingpolymer network having the desired elasticity and elastic memorycharacteristics.

The following chart lists various monomers which after purification, asby vacuum distillation, may be used in preparing the desired copolymerof crosslinked acrylic material as well as the concentration ranges forsuch monomers in percent by weight and preferred compositions I and IIin percent by weight composition.

    ______________________________________                         Preferred                   Concentration                               Compositions %    Monomer        Range %     I        II    ______________________________________    Ethyl Methacrylate                   25-15       34       34    Trifluoro Ethyl                    5-25       10       10    Methacrylate    n-Butyl Acrylate                   30-60       52       0    Ethyl Acrylate 30-60       0        52    2-Ethyl Hexyl Acrylate                   30-60       0        0    2-Hydroxy 4-Ethyloxy-                    0-10       1.5      1.5    Acryloxy Benzophenone    (UV-2098)    2,5 Dimethyl-2,5                   0.05-0.2    0.15     0.15    Bio (2-Ethyl Hydroxyl    Droxyl) Hexane (USP 245)    Ethylene Glycol                   0.5-3.0     2.5      2.5    Dimethyacrylate    ______________________________________

A preferred form of the method for forming the copolymer is depicted inFIG. 7. As there represented, ethyl methacrylate is mixed with n-butylacrylate or ethyl acrylate preferably in a weight percent concentrationof 34% to 52% respectively. In addition to the methacrylate and acrylateesters of ethyl methacrylate and n-butyl acrylate or ethyl acrylate, themixture includes 10% by weight of a fluoroacrylate functioning as asurface energy lowering agent. Such fluoroacrylates may be perfluorooctal methacrylate or more preferably trifluoroethyl methacrylate. Inthe mixture, the n-butyl acrylate or ethyl acrylate provides flexibilityin the presence of methacrylate esters principally because of the lowglass transition temperature thereof. However, the n-butyl acrylate orethyl acrylate renders the mixture tacky or sticky. Such tackiness isminimized by the fluoracrylate particularly trifluoroethyl methacrylate.In addition to the foregoing, and as represented in FIG. 7, the mixtureincludes a UV-absorber, UV-2098 and a free radical initiator, preferablyUSP 245, which is one in a class of aliphatic peroxides. The UV-absorberand initiator are present at 1.5 and 0.05% by weight concentrations. Thecombination is mixed, deaerated and placed in an oven at about 60° C.for two hours. The mixture undergoes partial polymerization to form aviscous syrupy liquid when cooled to about 25° C. The viscous syrupyliquid may be stored for several days at -15° C. for subsequent mixingwith a crosslinking agent and free radical initiator.

An alternate method of preparing the syrup is to dissolve low molecularweight (number average molecular weight between 30,000-50,000) polymerssuch as poly(ethyl methacrylate) and poly(n-butyl acrylate) in the samerelative concentrations at a polymer - monomer ratio ranging from 1:5 to1:3. The syrup may be filtered through a 0.2 micron filter immediatelyprior to use.

Again, as represented in FIG. 7, the crosslinking agent may consist ofethylene glycol dimethacrylate. Alternatively, the crosslinking agentmay be propylene glycol dimethacrylate or ethylene glycol diacrylate. Ineach case, the crosslinking agent is mixed in a weight percentconcentration of about 2.5 to produce a crosslinked density for theresulting copolymer in a range of . .0.5×10⁻² to 1.5×10⁻² .!..Iadd.0.23×10⁻¹ and 1.66×10⁻¹ .Iaddend.moles per liter. Such acrosslinking density provides the resulting polymer with the desiredelastic memory and elasticity. In particular, upon being folded, theresulting lens bodies 16 will return to its initial state naturally inabout 20 to 180 seconds and preferably about 30 seconds.

To produce an IOL 10 with the lens body 16 having the foregoingcharacteristics, and as further depicted in FIGS. 7, 8A and B and 9, thesyrup, crosslinking agent and initiator (in the indicated percent byweight concentrations) are mixed, deareated and the resulting mixturepoured into a mold such as mold number 1 or 2 illustrated in FIG. 8A andB or the mold illustrated in FIG. 9. With respect to molds of FIG. 8,the resulting mixture is poured onto an aluminum plate 1 bounded byrubber gaskets 2. A glass plate 3 is placed on top of the rubber gasketsand the combination clamped together by clamps 4. The mold is placed inan oven, heated to about 60° C. and cured for about 16 hours. The moldis then post cured at about 90° C. for 24 hours.

After curing, the mold is disassembled and the sheets formed thereinmade ready for cutting into cylindrical lens blanks in the case of moldnumber 1 for deflashing into lens bodies in the case of mold number 2.Alternatively, the mold bottom shown in FIG. 9 may be used. Asillustrated, the mold has slots machined into its aluminum base toaccommodate the haptics at an appropriate angle. The molded part fromthe mold of FIG. 9 comprises the optic and the haptic elements encasedin a thin sheet of flash which may be machined off to produce thefinished IOL.

Such cutting and machining to produce the desired IOL may involveconventional milling and lathe techniques with the exception that thepart is held at a temperature well below room temperature and preferablybetween -80° and -10° C. Specifically, it is desired that the materialbe held below its Beta-relaxation temperature during cutting.Preferably, during cutting, the low temperature environment is formed byexposing the part to a liquid nitrogen spray which maintains the partwithin the desired temperature range and provides the desired moisturefor the cutting operation. As previously noted, at or below itsBeta-relaxation temperature, the copolymer material possesses aparticularly hard characteristic suitable for high speed and efficientcutting.

An example of a procedure used to fabricate a multi-piece IOL as shownin FIG. 1 including separate haptics is as follows. First, flat sheetsof the crosslinked acrylic are molded at a thickness of between 2 mm and8 mm as described above and mounted on holders. The material is then cutinto disks which are lathe cut at the low temperatures previouslydescribed to form the curved planar surfaces and edge cut. The resultinglens bodies are soaked in Freon and chlorofluoro hydrocarbon solventsfor 20 minutes and then dried for 30 minutes in a vacuum oven at 60° C.The curved surfaces of the lens bodies are then polished at a lowtemperature. Next, the lens bodies are mounted for drilling of thepositioning holes 32 as well as the edge holes for receiving the haptics18. The positioning holes are typically 0.3 mm while the edge holes forreceiving the haptics are typically 0.1 mm in diameter. To mount thehaptics into the edge holes, the haptics are located in a stainlesssteel needle and one end of the haptic melted to form a thickened blunttip. The needle is then inserted into the edge hole to force the bluntend of the haptic into the hole at room temperature. The needle iscarefully withdrawn allowing the walls of the edge hole to collapse backto their normal position clamping the haptic in place. This operation isthen repeated for the other haptic.

Alternatively, for lens bodies molding using mold number 2 illustratedin FIG. 8B, the sheet is cored in the area of the lens bodies to cut thelens bodies from the sheet. The resulting lens bodies are then mountedin suitable holders and the foregoing procedure repeated.

Finally, for parts molded from the mold illustrated in FIG. 9, the flashmay be removed on a mill to form the desired one piece IOL.

From the foregoing, it should be appreciated that the IOLs of thepresent invention may be provided in various geometries adapted forfolding or rolling, etc. to a reduced profile configuration therebypermitting implantation into the eye through an incision of reducedsize. Within the eye, the deformed lens returns to its originalnondeformed state. However, according to the invention, the lens isformed from a material having a combination of excellent elastic memoryand slow speed of retraction characteristics. The lens thus returnsslowly to the nondeformed state without injuring eye tissue whileachieving the final nondeformed state without creases, wrinkles, orother structural deviations which would otherwise result in opticaldistortions.

A variety of further modifications and improvements to the inventiondescribe herein are believed to be apparent to those skilled in the art.Accordingly, no limitation is intended by way of the description herein,except as set forth in the appended claims.

I claim:
 1. A deformable-elastic intraocular lens (IOL), comprising:adeformable-elastic lens body of crosslinked acrylic material comprisingcopolymers of methacrylate and a acrylate esters which are relativelyhard and . .relative.!. .Iadd.relatively .Iaddend.soft at bodytemperature, crosslinked with a diacrylate ester wherein the crosslinkedacrylic material has a substantially tack-free surface, a crosslinkdensity of between . .0.5×10⁻² and 1.5×10⁻² .!. .Iadd.0.23×10⁻¹ and1.66×10⁻¹ .Iaddend.moles per liter, a glass transition temperaturebetween -30° and 25° C., a tensile modulus between 1000 and 3000 psi andan elongation at break of at least 100%; and flexible haptics attachedto the lens body to position the lens body in the eye.
 2. The IOL ofclaim 1 wherein the lens body is formed by chemically crosslinking thediacrylate ester with a partially polymerized mixture of the copolymers,curing the crosslinked acrylic and holding the cured crosslinked acrylicat a temperature below its Beta-relaxation temperature while machiningthe lens body.
 3. The IOL of claim 2 wherein each haptic is attached byforcing an enlarged end thereof into a smaller hole in an edge of thelens body.
 4. A deformable-elastic intraocular lens (IOL), comprising:adeformable-elastic lens body of crosslinked acrylic material formed bymixing copolymers of methacrylate and acrylate esters which arerelatively hard and relatively soft at body temperature, with adiacrylate ester to produce an acrylic material having crosslinkeddensity of between . .0.5×10⁻² and 1.5×10⁻² .!. .Iadd.0.23×10⁻¹ and1.66×10⁻¹ .Iaddend.moles per liter and a glass transition temperature ofbetween -30° and 25` C.; and flexible haptics attached to the lens bodyto position the lens body in the eye.
 5. The IOL of claim 4 wherein thecopolymers are mixed and partially polymerized before mixing with thediacrylate ester.
 6. A deformable-elastic intraocular lens body of acrosslinked acrylic material comprising copolymers of methacrylate andacrylate esters which are relatively hard and relatively soft at bodytemperature, crosslinked with a diacrylate ester wherein the acrylicmaterial has a substantially tack-free surface, a crosslink density ofbetween . .0.5×10⁻² and 1.5×10⁻² .!. .Iadd.0.23×10⁻¹ and 1.66×10⁻¹.Iaddend.moles per liter, a glass transition temperature between -30°and 25° C., a tensile modulus between 1000 and 3000 psi and anelongation at break of at least 100%.
 7. A deformable-elasticintraocular lens body of a crosslinked acrylic material formed byreacting copolymers of methacrylate and acrylate esters which arerelatively hard and relatively soft at body temperature to produce areaction product having a glass transition temperature between -30° and25° C., partially polymerizing the reaction product and mixing it with adiacrylate ester to produce a crosslinked acrylic having a crosslinkdensity of between . .0.5×10⁻² and 1.5×10⁻² .!. .Iadd.0.23×10⁻¹ and1.66×10⁻¹ .Iaddend.moles per liter, curing the acrylic and machining thelens body therefrom.
 8. The lens body of claim 7 wherein the relativelyhard methacrylate ester is a fluoroacrylate.
 9. The lens body of claim 7wherein reaction product comprises ethyl methacrylate, trifluoro ethylmethacrylate and an acrylate ester present in percent by weightconcentrations of 25 to 45, 5 to 25 and 30 to 60%, respectively.
 10. Thelens body of claim 9 wherein the acrylate ester is selected from n-butylacrylate, ethyl acrylate and 2-ethyl hexyl acrylate.
 11. The lens bodyof claim 10 wherein the diacrylate ester is present in a percent byweight concentration of 0.5 to 3.0%.
 12. The lens of body of claim 11wherein the diacrylate ester is selected from ethylene glycoldimethacrylate, propylene glycol dimethacrylate, and ethylene glycoldiacrylate.
 13. A method of forming a deformable-elastic intraocularlens body comprising the steps of:(a) mixing copolymers of methacrylateand acrylate ester which are relatively hard and relatively soft at bodytemperature; (b) partially polymerizing the product of Step (a); (c)chemically crosslinking the product of Step (b) with a diacrylate ester;(d) curing the product to Step (c); and (e) forming a lens body having apredetermined optical characteristic from the product of Step (d). 14.The method of claim 13 wherein Step (e) comprises holding the product ofStep (d) at a temperature below its Beta-relaxation temperature whilemachining the lens body.
 15. The method of claim 13 wherein themethacrylate and acrylate esters are mixed together in approximately a45 to 55% by weight ratio.
 16. The method of claim 15 wherein thediacrylate ester of Step (C) is present in a percent composition byweight of 0.5 to 3.0%.
 17. The method of claim 16 further including themixing of a UV-absorber and a free radical initiator in Step (a). 18.The method of claim 13 wherein the relatively hard methacrylate ester isa fluoroacrylate.
 19. The method of claim 18 wherein Step (a) furtherincluding mixing the fluoroacrylate in a concentration range by weightof between 5 and 25% with ethyl methacrylate in a concentration range byweight of between 25 and 45% and an acrylate ester selected from n-butylacrylate, ethylacrylate or 2-ethyl hexyl acrylate in a concentrationrange by weight of between 30 and 60%.
 20. The method of claim 19wherein the fluoroacrylate is trifluoro ethyl methacrylate.
 21. Themethod of claim 20 wherein Step (a) further includes the mixing of aUV-absorber in a concentration range by weight of between 0 and 10% anda free radical initiator in a concentration range by weight of 0.05 and0.2%.